Clayton Kershaw, who signed a $215 million, seven-year contract on Jan. 15, will be on the DL for the first time in his career.(AP IMAGES)

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ANAHEIM, Calif. — Los Angeles Dodgers ace Clayton Kershaw was placed on the 15-day disabled list Saturday for the first time in his seven-year career because of a swollen muscle in his left upper back.

The 26-year-old left-hander, coming off his second Cy Young Award in three years, already had been scratched from his scheduled start in San Diego on Sunday after an MRI revealed the problem.

Kershaw was on a throwing progression program and was tossing the ball at different distances Saturday before the team's Freeway Series finale against the Angels when he experienced some discomfort on his 27th throw.

"He felt it, and that was the last straw," manager Don Mattingly said. "So at that point, we knew we couldn't have gone any farther and that it was a DL situation. It's a situation — not just for me, but for everyone — that we've got to save Clayton from Clayton at this point and be cautious. We can't allow him to try to keep pushing and go forward. If it was up to him, I'm sure he'd want to go farther. But we can't allow him to do that right now."

Kershaw, who signed a $215 million, seven-year contract on Jan. 15, won the Dodgers' season opener 3-1 against the Arizona Diamondbacks in Australia last weekend.

The three-time All-Star was hoping to get back in the rotation for Friday's home opener against San Francisco, but instead it will be Hyun-Jin Ryu, who also will get the assignment Sunday at San Diego against Andrew Cashner. Ryu started and won the second game of the Australia trip, but tore a toenail while running the bases that day and wasn't sure he'd be able to fill in for Kershaw until after his side session Friday.

"I think that once Clayton felt something, he knew that he wasn't going to make his start on Friday," Mattingly said. "With his throwing progression, the fact that he stopped right away is all we've asked of him from the beginning: 'If you feel it at all, you've got to stop.' And he stopped right away."

Kershaw has made 33 starts, struck out at least 229 batters and logged 227 2/3 innings or more in each of the last three seasons — including a career-high 236 innings last year, when he finished 16-9 with an NL-best 232 strikeouts and a 1.83 ERA.

Kershaw led the majors in ERA for the third straight year, becoming the first pitcher to accomplish that feat since newly elected Hall of Famer Greg Maddux did it from 1993-95.

Now that Kershaw's run at a fourth straight ERA title has been adjourned for the time being, Mattingly wasn't making any predictions on when he will return to the rotation. The Dodgers have five off days scheduled between now and April 15.

"This is not something that we say, 'OK, we think he'll be ready by this date' — and if he doesn't get there, then it's like, 'Oh, Clayton's had a setback,'" Mattingly said. "We should just let it do what it's supposed to do and let the medical staff do their work let them tell us what he could do.

"And because of all the days off we have and the schedule we have, it's really not worth pushing him."